Contemporary fluid dispense systems are well suited for dispensing precise amounts of fluid at precise positions on a substrate. A pump transports the fluid to a dispense tip, also referred to as a xe2x80x9cpinxe2x80x9d or xe2x80x9cneedlexe2x80x9d, which is positioned over the substrate by a micropositioner, thereby providing patterns of fluid on the substrate as needed. As an example application, fluid delivery systems can be utilized for depositing precise volumes of adhesives, for example, glue, resin, or paste, during a circuit board assembly process, in the form of dots for high-speed applications, or in the form of lines for providing underfill or encapsulation.
Contemporary dispensing pumps comprise a syringe, a feed tube, a dispense cartridge, and pump drive mechanism. The syringe contains fluid for dispensing, and has an opening at its distal end at which a feed tube is connected. The feed tube is a flexible, hollow tube for delivering the fluid to the cartridge. The cartridge is hollow and cylindrical and includes an inlet neck at which the opposite end of the feed tube is connected. The inlet neck directs the fluid into the hollow, central cartridge chamber.
A feed screw disposed longitudinally through the center of the cylindrical chamber transports the fluid in Archimedes principle fashion from the inlet to a dispensing needle attached to the chamber outlet. A continuously-running motor drives the feed screw via a rotary clutch, which is selectively actuated to engage the feed screw and thereby effect dispensing. A bellows linkage between the motor and cartridge allows for flexibility in system alignment.
Pump systems can be characterized generally as xe2x80x9cfixed-zxe2x80x9d or xe2x80x9cfloating-zxe2x80x9d (floating-z is also referred to as xe2x80x9ccompliant-zxe2x80x9d). Fixed-z systems are adapted for applications that do not require contact between the dispense tip and the substrate during dispensing. In fixed-z applications, the dispense tip is positioned and suspended above the substrate by a predetermined distance, and the fluid is dropped onto the substrate from above. In floating-z applications, the tip is provided with a standoff, or xe2x80x9cfootxe2x80x9d, designed to contact the substrate as fluid is delivered by the pump through the tip. Such floating-z systems allow for tip travel, relative to the pump body, such that the entire weight of the pump does not bear down on the substrate.
Such conventional pump systems suffer from several limitations. The motor and rotary clutch mechanisms are bulky and heavy, and are therefore limited in application for modern dispensing applications requiring increasingly precise, efficient, and fast operation. The excessive weight limits use for those applications that require contact of the pump with the substrate, and limits system speed and accuracy, attributed to the high g-forces required for quick movement of the system. The mechanical clutch is difficult to control, and coasts to a stop when disengaged, resulting in deposit of excess fluid. Clutch coasting can be mitigated by a longitudinal spring mounted about the body of the feed screw and urged against the chamber end to offer rotational resistance. However, the spring adds to the length of the cartridge, and contributes to system complexity.
The inlet neck feeds directly into the side of the feed screw or xe2x80x9caugerxe2x80x9d. Consequently, as the auger collects material from the small and circular inlet port, high pressure is required for driving the material into the auger body, because the auger threads periodically pass in front of the feed opening, preventing material from entering. This leads to inconsistent material flow. Additionally, the inlet neck is commonly perpendicular to the auger screw, requiring the fluid to make a 90 degree turn upon entering the pump. This further limits material flow and can contribute to material xe2x80x9cballingxe2x80x9d and clogging.
Overnight storage of dispensed fluids often requires refrigeration of the fluid and cleaning of the system. The syringe is typically mounted directly to a mounting bracket on the pump body such that the output port of the syringe passes through an aperture on the mounting bracket. The feed tube is then coupled to the output port on the opposite face of the bracket. Since the tube and bracket are on opposite sides of the bracket, removal of the syringe from the pump body requires dismantling of the tube and syringe, which can contaminate fluid material positioned at the interface during disassembly. Further, since the syringe and cartridge can not be removed and stored together as a unit, disassembly and cleaning of the cartridge is required. Additionally, the inlet neck is narrow and therefore difficult to clean.
The present invention is directed to a fluid pump and cartridge system that overcomes the limitations of conventional systems set forth above.
In a first aspect, the present invention is directed to a cartridge adapted for use with a fluid pump. The cartridge includes a material inlet port, a material outlet port, a feed screw, and a reservoir. The feed screw is disposed longitudinally through the body of the cartridge for delivering fluid provided at the inlet port to the outlet port. The inlet port takes the form of an elongated port provided at a side portion of the feed screw proximal to allow for fluid provided at the inlet port. This elongated configuration promotes even distribution of fluid during transport by the feed screw, and lowers system pressure, thereby reducing the likelihood of xe2x80x9cballing-upxe2x80x9d and/or clogging of fluid.
The inlet port is preferably provided through the cartridge body at an acute angle relative to the reservoir to allow for gravity-assisted fluid delivery. The inner portion of the cartridge may be lined with a carbide or plastic (for example Teflon, torlon, or tercite) liner having an aperture aligned with the inlet port to enhance ease of cleaning. The elongated port of the cartridge may be provided in a wall of the carbide liner.
In another aspect, the present invention is directed to a release bracket for mounting the syringe and cartridge to the body of the pump. In this manner, the syringe, feed tube, and cartridge can be dismantled from the pump body as a unit, allowing for joint storage of the syringe, feed tube and cartridge, while minimizing risk of contamination of the material. Additionally, once the system is initially purged of extraneous gas during initialization, the purged system can be stored as a unit without the need for re-initialization prior to its next use.
In another aspect, the present invention is directed to a fluid pump assembly that employs an electronically-operated servo-motor assembly. A closed-loop servo motor having a rotary encoder is adapted for controlling rotation and position of the feed screw with heightened accuracy, as compared to those of conventional clutch-driven assemblies. For example, in a preferred embodiment, a rotary encoder capable of 8000 counts in a 360 degree range may be employed to achieve dispensing resolution to a degree that is orders of magnitude greater than conventional systems. Servo-motor-based systems further confer the advantages of small, lightweight systems well-suited for high-performance operation. Electronic control allows for complete determination of the acceleration/deceleration of feed screw rotation, allowing for application-specific flow profiles. An orbital gear transmission unit may be provided between the motor and the pump feed screw for providing further accuracy in controlling the feed screw.
In another aspect, the present invention is directed to a pump assembly that is compatible with both floating-z and fixed-z cartridges and dispensing tips. A quick-release pin, which may be spring-biased, is provided on the side of the cartridge body to allow for removal/insertion of cartridges. A fixed-z cartridge includes a hole for receiving the quick-release pin in a fixed relationship. A floating-z cartridge includes a longitudinal groove to permit longitudinal travel of the pin in the groove, and thus allow for floating-z operation.
In another aspect, the present invention is directed to a quick-release mount assembly for mounting a pump to a dispensing frame. The pump body includes a tab feature on its surface for mating with a hole on a mounting plate attached to the dispensing frame. The mounting plate includes a lever for securing the tab when inserted. Guide features may be provided for aligning and guiding the pump body relative to the mounting plate.
In another aspect, the present invention is directed to an apparatus and method for drawing entrapped air from the material supply during a dispensing operation, thereby purging the system of entrapped air. A vacuum is drawn from the material supply, for example by a vacuum tube with needle inserted into a material feed tube, in a direction parallel to material flow through the feed tube. In this manner, air is withdrawn from the dispensed material, leading to an improvement in dispensing consistency, especially at small tolerances.
In another aspect, the present invention is directed to a vacuum purge configuration for removing air entrapped in the body of the cartridge during initialization of a dispensing operation. A first purge interface is placed on the end of the feed tube, and a vacuum is drawn, thereby purging the feed tube of entrapped gas. A second purge interface is then placed on the cartridge body outlet while the feed screw is rotated slowly until material presents itself at the outlet. A vacuum is drawn to eliminate entrapped gas from the cartridge. A third purge interface is then placed on the needle assembly and a vacuum is drawn to eliminate entrapped air from the needle body. Entrapped air is thus substantially removed from the feed tube, auger screw and dispensing needle. Normal dispensing can commence following removal of the purge interface.
In another aspect, the present invention is directed to a bellows means inserted at the piston end of, and replacing the piston of, a dispensing syringe. The bellows is pressurized from within and expands, thereby exerting pressure on the underlying material, forcing material flow. In this manner, material can be driven with minimal pressure, and with minimal air migration into the material, as compared to plunger-style drivers. In a preferred embodiment, the bellows comprises a latex film applied about the lip of the syringe top. The syringe top is preferably vented to allow for expansion of the bellows.
In another aspect, the present invention is directed to a pump cartridge having a material feed aperture that is elongated with respect to the primary axis of the feed screw. In this manner, a larger portion of the feed screw threads are exposed to the material supply, leading to improvement in dispensing consistency. In a preferred embodiment, a carbide cartridge liner is inserted in the cartridge cavity between the cartridge body and the feed screw, and the elongated aperture is provided in the body of the carbide insert to provide increased material supply exposure.